FIG. 1 shows a structure of a conventional armature of this kind, in which the reference numeral 1 designates a face-type commutator constituted by disc-like commutator segments 2 and a resin-molding member 3 which is molded so as to engage with the commutator segments 2 by engagement claws 2a of the latter so that the commutator segments 2 and the resin-molding member 3 are integrated with each other. To commutator 1 is fixed to an armature rotary shaft 5 through a bush 4. The refernce numeral 6 designates armature coils inserted and held in slots provided in a core 7. End portions of the coils 6 are inserted in riser grooves 8 of the commutator segments 2 so as to be electrically connected to the commutator segments 2. The core 7 is fixed to the armature rotary shaft 5. The reference numeral 9 designates binding wire wound around the outer circumference of the armature coils 6 through insulating paper 10. The binding wire 9 is provided to prevent the coils 6 from floating up owing to centrifugal force when the armature is rotated.
Upon turning a key switch on in the engine starter using such an armature, a current is caused to flow from brushes (not-shown) which are in contact with the commutator segments 2 into the armature coils 6 through the commutator segments 2 so that rotary force is generated in the armature. The rotary force is transmitted to a ring gear (not shown) of the engine so as to be able to start the engine. Although centrifugal force acts on the armature coils 6 in a direction so as to make the armature coils 6 come off from the commutator segments 2 as the armature is rotated, the armature coils 6 are prevented from floating up by the binding wire 9. Such a conventional armature however has a problem in that when the armature is rotated at a high speed, the centrifugal force acting on the commutator segments 2 is so great that it becomes impossible to keep the commutator segments 2 fixed to the resin-molding member 3 solely by the holding force of the engaging claws 2a thus allowing the commutator segments 2 to come off from the resin-molding member 3 so as not to operate as an armature.
The present invention has been attained to eliminate the problems as described above, and an object thereof is to obtain an armature of an electric motor in which separation of the commutator segments from resin-molding member owing to the centrifugal force can be prevented from occurring.